Space Shuttle prototype testing. Test flight for prototype Space Shuttle Enterprise. After its release from NASA's 747 Shuttle Carrier Aircraft (SCA), Enterprise glided back to NASA's Dryden Flight Research Center (Edwards Air Force Base in background), California, USA. With a crew of two (Joe Engle and Richard Truly), this was the fourth of the five free-flight flights in the Shuttle's Approach and Landing Tests (ALT) program. The tests prepared for the first space mission with the Space Shuttle Columbia in April 1981. The Space Shuttles flew 135 missions into low Earth orbit between 1981 and 2011. Photographed on 12 October 1977.